1. Field of Invention
This invention relates generally to a toner concentration sensor usable in an electrophotographic printing machine.
2. Description of Related Art
U.S. Pat. No. 6,006,047, the subject matter of which is incorporated herein by reference in its entirety, discloses an apparatus that monitors and controls an electrical parameter of an imaging surface. The monitor controlling apparatus includes a patch generator that records on the imaging surface a first control patch at a first voltage level and a second control patch at a second voltage level. This apparatus also includes an electrostatic volt meter that measures voltage potentials associated with the first and second control patches. A processor, in communication with the patch generator, calculates electrical parameters of the imaging surface from the measured voltage potentials from the first and second control packages. The processor determines a deviation between the calculated electrical parameter values and setup values.
The processor then produces and sends a feedback error signal to the patch generator if the deviation exceeds a threshold level. The patch generator then records a third control patch at a third voltage level on the imaging surface in response to receiving the error signal. The electrostatic volt meter senses the third control patch. The processor calculates the electrical parameters of the imaging surface from the measured voltage potential of the third control patch and determines a correction factor. The charging device, exposure system and developer are adjusted based on this correction factor. The three patch sequence is repeated until convergence on a desired value is achieved.
U.S. Pat. No. 5,895,141, the subject matter of which is incorporated herein by reference in its entirety, discloses a toner concentration control system which determines when the charge between the developer material particles, that is, the developer particles and the carrier particles, becomes weak. This results in initial copies which are darker than expected. To determine when this condition has occurred, this system develops two halftone calibration patches which are intended to have reflectivities of 12% and 87%, i.e., one patch reflects approximately 12% of the light incident thereon and the other patch reflects approximately 87% of the light incident thereon. The actual reflectance of these two patches is read by a black toner area coverage sensor and recorded. The measured reflectance difference between the two patches, such as, for example, 75% (12% minus 87%), is calculated. A large difference is a good indicator of whether the patches have become too dark. If the reflectance difference (delta) is less than a target value, the tribo is considered to be within an acceptable range and nothing is done. Tribo is shorthand nomenclature for the tribo-electric relationship between toner carrier particles and toner particles, i.e., wherein the toner particles have a polarity causing them to detach themselves from the carrier particles in charged portions of the image-bearing articles and be attracted to a photoconductive surface. If, however, the difference is greater than the target value, the print engine proceeds to perform a special rest recovery setup. The setup initially tones up and tones down the system enough to increase the toner triboelectric charge and rejuvenate the toner material. The system then continues with the regular setup steps of toner concentration setup and electrostatic convergence. Once completed, the system goes back online and is ready to produce good copy quality. The system disclosed in the 141 patent allows a toner concentration sensor to be eliminated.
U.S. Pat. No. 6,029,021, the subject matter of which is incorporated herein by reference in its entirety, discloses an image forming system having a dual component inversion developing system that forms a toner patch image. The toner patch image is used to determine the toner concentration and to control an image forming condition such as the toner concentration based on the density of the toner patch image. Two patches, a relatively small point patch image and another toner patch image, a band patch image, are formed on the image carrier. A concentration sensor detects light reflected from each of the point patch image and the band patch image. For each patch, an average value of the read detection values read by the concentration sensor is calculated. For each patch, a patch image concentration is calculated based on the average value detected for each patch and on the ratio between the average value and the detection value on a clean face of the photoreceptor.
Charge potential control, based on the point patch image concentration, that is; control of the toner concentration; is executed before executing a xerographic job, that is, during an interimaging interval. Toner concentration control based on the band patch image concentration is executed, for example, after the first job after the image forming system is powered on, or after outputting a predetermined number of sheets, such as, for example, 20 sheets, from after a previous concentration control event.
U.S. Pat. No. 6,035,152, the subject matter of which is incorporated herein by reference in its entirety, discloses a xerographic print engine that has process control systems and methods that adjust printing operations based on a tone reproduction curve which is setup based on test control patches.
As discussed above, toner concentration control typically involves creating a single toner patch on a single charged area of a photoreceptor. Even when multiple patches are formed, a single charge level is placed on the photoreceptor. However, the inventors have determined that the toner concentration curve between the toner concentration and the relative reflectivity is highly dependent on the charge level placed on the photoreceptor.
This invention provides systems and methods for determining an improved calibration curve for a toner concentration sensor.
This invention separately provides systems and methods for determining a plurality of calibration curves for a toner concentration sensor having different photoreceptor charge levels.
This invention further provides systems and methods for combining the plurality of calibration curves for the toner concentration sensor to form a composite calibration curve.
This invention additionally provides systems and methods that determine an average calibration curve from the plurality of calibration curves.
This invention separately provides systems and methods for charging a photoreceptor to different charge levels when determining different calibration curves for a toner concentration sensor.
This invention separately provides systems and methods that determine a plurality of calibration curves for a toner concentration sensor where each calibration curve is responsive over a distinct toner concentration range.
This invention additionally provides systems and methods that determine each of the calibration curves that are responsive over a distinct toner concentration range using a distinct charge level on the photoreceptor.
The systems and methods according to this invention concern xerographic print engines that employ a toner concentration sensor. In various exemplary embodiments, the systems and methods according to this invention prepare a toner concentration calibration curve by developing toner concentration patches with different toner concentrations and calibrate a toner concentration sensor to actual system development response by operating the toner concentration sensor at two or more different operating points. In various exemplary embodiments, for example, the two different operating points are two extreme development voltage levels where the toner concentration sensor provides most sensitive data.
In various exemplary embodiments, the systems and methods according to this invention use the print engine light source, which is already in the print engine, to generate continuous tone 100% area coverage patches at two different operating points for the calibration. In various exemplary embodiments, the patches are developed multiple times using developer which has varying amounts of toner, i.e., using different toner concentrations. In various exemplary embodiments, the relative reflectivities of the different patches developed using different amounts of toner are graphed with respect to the toner concentrations to obtain a number of distinct toner concentration sensitivity curves. In various exemplary embodiments of the systems and methods according to this invention, an average toner concentration curve is determined based on the number of distinct toner concentration sensitivity curves. By calibrating the toner concentration sensor according to the invention, greater component latitude and the ability to maintain high image quality for high end printing systems for a longer time can be obtained.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.